Modified Variable Temperature Stage as a Microwave Power Meter for Cryogenic Environments

We present a novel approach to realize a microwave power meter suitable for cryogenic environments, based on a modified Variable Temperature Stage (VTS). The method exploits the AC/DC transfer of power, thereby providing traceability to voltage and current standards. A weakly thermally coupled variable-temperature platform is implemented inside a dilution cryostat (base temperature <20 mK), where two heating modalities — microwave (AC) and direct resistive (DC) excitation — are applied and compared. Under reasonable assumptions, the input powers delivered by the two methods are considered equivalent, enabling a cross-comparison of the two approaches, leading to an inferred microwave power measurement. The system operates as a pass-through power meter, allowing readout during experiments. To achieve this functionality, an attenuator is integrated as the power-absorbing element instead of a matched load, and its impact on the measurement is assessed through scattering-parameter analysis. A preliminary evaluation of the usable microwave power range, system sensitivity, and thermalization dynamics is presented, with particular focus on response times and equilibration scales. The results demonstrate the feasibility of a traceable, in-situ microwave power measurement solution for quantum devices operating at millikelvin temperatures.